AP Biology : Understand light independent reactions (Calvin cycle)

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #1 : Understand Light Independent Reactions (Calvin Cycle)

Where does the Calvin Cycle take place?

Possible Answers:

Stroma

Thylakoid membrane

Cytoplasm

Chloroplast outer membrane

Mitochondrial lumen

Correct answer:

Stroma

Explanation:

The Calvin Cycle (dark reactions) take place in the stroma of the chloroplasts, which is the aqueous space inside the organelle. 

Example Question #2 : Understand Light Independent Reactions (Calvin Cycle)

Where does the Calvin cycle take place in the chloroplasts?

Possible Answers:

Nucleus

Mitochondria

Stroma

Thylakoid

Correct answer:

Stroma

Explanation:

The Calvin cycle takes place in the stroma area in the chloroplasts. The mitochondria is another organelle, and the nucleus contains the DNA. The thylakoids are in the chloroplasts and contain the pigment chlorophyll in which the light reactions occur.

Example Question #1 : Photosynthesis

What is the name of the light-independent reaction of photosynthesis?

Possible Answers:

Glycolysis

Calvin cycle

Beta-oxidation

Krebs cycle

Correct answer:

Calvin cycle

Explanation:

The light-independent reaction in photosynthesis is called the Calvin cycle. Glycolysis and the Krebs cycle are the first and second steps in cellular respiration, respectively. Beta-oxidation is the process by which fatty acids are broken down into acetyl-CoA, which may enter the Krebs cycle, ultimately to produce ATP.

Example Question #1 : Understand Light Independent Reactions (Calvin Cycle)

Which is not a step of the light independent reaction?

Possible Answers:

regeneration of RuBP

carbon fixation

production of G3P

light absorption in photosystem II

Correct answer:

light absorption in photosystem II

Explanation:

Absorption of sunlight in photosystem II is the first step of the light dependent reaction, not the light independent reaction. During the light independent reaction, or the Calvin Cycle, carbon fixation first occurs. CO2 produced during the light dependent reaction reacts with RuBP, ultimately producing PGA. This reaction is catalyzed by the enzyme Rubisco. Then, PGA is converted to G3P, using ATP and NADPH produced during the light dependent reaction. The G3P is ultimately converted to glucose. Every 3 cycles of the Calvin Cycle (light independent reaction), 6 molecules of G3P are produced; only 1 is used to produce glucose. The remaining 5 molecules of G3P are used to regenerate RuBP to allow the Calvin Cycle to continue.

Example Question #1 : Understand Light Independent Reactions (Calvin Cycle)

Where do light independent reactions of photosynthesis occur?

Possible Answers:

nucleus

thylakoid of chloroplasts

stroma of chloroplasts

ribosome

Correct answer:

stroma of chloroplasts

Explanation:

Light independent reactions occur in the stroma of the chloroplasts. Light dependent reactions occur in the thylakoid membrane.

Example Question #6 : Understand Light Independent Reactions (Calvin Cycle)

What the products of the light independent reactions?

Possible Answers:

CO2, NADPH, ATP

glucose, NADPH, H2O

glucose, NADP+, H2O

O2, NADP+, ATP

Correct answer:

glucose, NADP+, H2O

Explanation:

Light independent reactions occur in the stroma of the chloroplasts. Light dependent reactions occur in the thylakoid membrane.

Example Question #2 : Understand Light Independent Reactions (Calvin Cycle)

What the products of the light independent reactions?

Possible Answers:

glucose, NADP+, H2O

glucose, NADPH, H2O

O2, NADP+, ATP

CO2, NADPH, ATP

Correct answer:

glucose, NADP+, H2O

Explanation:

The products of the light independent reaction are glucose, NADP+, and H2O. The reactants are CO2, NADPH, and ATP.

Example Question #3 : Photosynthesis

Which enzyme is important in photosynthesis, and what is its function?

Possible Answers:

amylase; carbon fixation during the first step of light independent reaction

oxidase; captures energy from the sun during light dependent reaction

ribulose bisphosphate carboxylase; captures energy from the sun during light dependent reaction

ribulose bisphosphate carboxylase; carbon fixation during the first step of light independent reaction

Correct answer:

ribulose bisphosphate carboxylase; carbon fixation during the first step of light independent reaction

Explanation:

During the first step of the light independent reaction, or Calvin Cycle, CO2 produced from the light dependent reaction reacts with RuBP. This reaction is catalyzed by Rubisco, or ribulose bisphosphate carboxylase.

Example Question #9 : Understand Light Independent Reactions (Calvin Cycle)

Which is not a required input for the Calvin Cycle?

Possible Answers:

sunlight

CO2

NADPH

ATP

Correct answer:

sunlight

Explanation:

The Calvin Cycle, or light independent reaction, does not utilize sunlight as an input. During the light independent reaction, or the Calvin Cycle, carbon fixation first occurs. CO2 produced during the light dependent reaction reacts with RuBP, ultimately producing PGA. This reaction is catalyzed by the enzyme Rubisco. Then, PGA is converted to G3P, using ATP and NADPH produced during the light dependent reaction to allow this reaction to occur. The G3P is ultimately converted to glucose. Every 3 cycles of the Calvin Cycle (light independent reaction), 6 molecules of G3P are produced; only 1 is used to produce glucose. The remaining 5 molecules of G3P are used to regenerate RuBP to allow the Calvin Cycle to continue.

Example Question #10 : Understand Light Independent Reactions (Calvin Cycle)

How many G3P molecules are produced after 3 cycles of the Calvin Cycle; and how many of these G3P molecules are used to produce glucose after 3 cycles of the Calvin Cycle?

Possible Answers:

1; 1

3; 1

6; 3

6; 1

Correct answer:

6; 3

Explanation:

Every 3 cycles of the Calvin Cycle (light independent reaction), 6 molecules of G3P are produced; only 1 is used to produce glucose. The remaining 5 molecules of G3P are used to regenerate RuBP to allow the Calvin Cycle to continue.

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